1. Field of the Invention
The present invention relates to an image pickup system, and more particularly, to an image pickup system which can generate a new image for display using two types of images and detect a white spot pixel.
2. Description of the Related Art
Conventionally, in an image pickup system including a solid-state image pickup device, there is a case where a pixel defect referred to as a so-called white spot occurs based on a crystal defect on an image pickup surface of the solid-state image pickup device. Because it is difficult to completely remove such a pixel defect, conventionally, efforts have been made to improve a yield ratio of the solid-state image pickup device by providing a pixel defect correction circuit and correcting an image.
For example, Japanese Patent Application Laid-Open Publication No. 10-322603 discloses a technique of detecting a defect pixel of a solid-state image pickup device using a pixel defect inspection apparatus when an image pickup system is shipped from the factory, recording position information of the defect pixel, and, then, correcting the pixel defect based on the recorded position information of the defect pixel.
Further, also in an endoscope system on which a solid-state image pickup device is mounted, conventionally, a technique of detecting and recording a white spot pixel and correcting the white spot based on the recorded information has been known.
Specifically, in a step of shipping an endoscope system from the factory, a white spot pixel is detected by picking up an image of a black object and determining an excess luminance value, and storing a position of the white spot pixel in an ID memory, or the like, mounted on an endoscope as address information of XY. Then, a technique is known in which, when the endoscope is used, predetermined correction processing is performed on the white spot pixel based on the address information stored in the ID memory at a connected processor or at the endoscope itself.
However, while the above-described correction of the white spot pixel effectively works on a pixel defect such as a white spot (white spot generated previously) which has been already generated upon shipping from the factory, it is difficult for the above-described correction to effectively work on a white spot pixel generated after shipment.
That is, it is known that a white spot pixel degrades over time because the white spot pixel is based on a crystal defect, or tends to increase in accordance with increase of the temperature. However, because the conventional detection of a defect pixel such as detection of a white spot is performed during a manufacturing stage as described above, the conventional detection cannot cope with change over time, or the like, of a defect pixel, which occurs later in the market after shipping.
As a technique for coping with change over time of a pixel defect after shipping from the factory, Japanese Patent Application Laid-Open Publication No. 2001-086411 discloses a technique of displacing an image formation position of light incident on a solid-state image pickup device by moving an optical member inserted into an optical path of an image pickup optical system, and detecting a pixel defect by comparing image data before and after a frame.
Further, Japanese Patent Application Laid-Open Publication No. 2009-232200 discloses a pixel defect correcting method of respectively picking up images of a plurality of dispersed light obtained by dispersing image pickup light, comparing video signals outputted by picking up images at the same image pickup position or the near image pickup position for each of the respective dispersed light, detecting whether or not a pixel defect occurs at the image pickup device which picks up an image of any of the dispersed light according to a comparison result, and performing correction.
On the other hand, conventionally, in an image pickup system which can acquire two types of images, a technique of generating a new image for display using the two types of images is put to practical use.
For example, as a technique of generating a stereo image using two types of picked up images having disparity, Japanese Patent Application Laid-Open Publication No. 2012-065204 and Japanese Patent Application Laid-Open Publication No. 2001-148865 disclose an image pickup apparatus which picks up a stereo image (3D image) using a plurality of image pickup units.
Further, Japanese Patent Application Laid-Open Publication No. 2003-032559 discloses a technique of generating an image for display having a high dynamic range using two types of picked up images having different luminance.
In the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2003-032559, one optical image is separated into two optical images by a light flux separating unit, and these two separated optical images are formed on an image pickup surface of one image pickup device. In this technique, two image pickup signals having different luminance are generated by performing photoelectric conversion on the two types of optical images on the image pickup device, and a high dynamic range image is acquired by converting the two image pickup signals into image signals and synthesizing the image signals.